1. Field of the Invention
The present invention relates to a solution casting process for producing polymer film. More particularly, the present invention relates to a solution casting process for producing polymer film of which quality of surfaces can be high.
2. Description Related to the Prior Art
JP-A 2001-315147 discloses a solution casting process for producing polymer film. Examples of polymer films include cellulose triacetate (TAC) film, and other cellulose acylate films. The solution casting process is widely used to manufacture a liquid crystal display panel, photosensitive material, and the like. Today, the liquid crystal display panel has been marketed more and more widely. So the production of the polymer film is required to have higher efficiency. For example, a casting speed of the solution casting process is desired to be higher. A thickness of the polymer film is desired to be smaller. To obtain the TAC film as the polymer film, at first the cellulose triacetate is dissolved in a mixed solvent of which a main component is dichloro methane, to prepare polymer solution or dope. The dope is cast on a supporting surface, to form gel film. After this, the gel film comes to have a self-supporting characteristic on the supporting surface. A stripping roller is actuated to strip the gel film to obtain self-supporting cast film. Rollers are rotated to feed the self-supporting cast film into a tenter drier machine. The self-supporting cast film is subjected to extension, dried, to produce the polymer film.
However, the solubility of the cellulose acylate to solvent is very low. Considerable difficulty lies in raising density of solid content in the dope being prepared. It is conceivable to raise a speed of solution casting or to reduce thickness of the polymer film for the purpose of raising productivity. However, shortcomings arise in low strength of the gel film, occurrence of curls in the self-supporting cast film before feeding to the tenter drier machine after stripping from the supporting surface, and occurrence of wrinkles on surfaces of the self-supporting cast film. A pair of lateral edge portions of the polymer film is supported inside the tenter drier machine without using rollers for the purpose of feeding. If curls occur on the lateral edge portions in the polymer film, a problem is likely to arise in an unstable state of the supporting operation of the lateral edge portions. If considerably large curls occur, there will be a failure in entry in the tenter drier machine. Continuous actuation of a system for producing the polymer film may be stopped accidentally. If wrinkles are created on the surfaces of the self-supporting cast film before being dried, residue of wrinkles will be present on the surfaces of the polymer film as a product, to lower the quality. This will cause a serious problem in that yield in the production will be too low due to temporarily low quality.